This body of studies seems to assume, and base conclusions on the assumption, that the tribal people don't get education - any education. Unless they go to a Western school. Even though the study results in the US and South America plainly show that schooling makes no difference, other than dampen non-Euclidian skills...
Supporting information: http://www.pnas.org/content/suppl/2011/05/19/1016686108.DCSupplemental/pnas.201016686SI.pdf
The researchers concluded that geometric understanding may not be dependent on language, but then extended their conclusions too far (or maybe I am misinterpreting it):
"The responses of Mundurucu adults and children converged with that of mathematically educated adults and children and revealed an intuitive understanding of essential properties of Euclidean geometry. For instance, on a surface described to them as perfectly planar, the Mundurucu's estimations of the internal angles of triangles added up to ∼180 degrees, and when asked explicitly, they stated that there exists one single parallel line to any given line through a given point. These intuitions were also partially in place in the group of younger US participants. We conclude that, during childhood, humans develop geometrical intuitions that spontaneously accord with the principles of Euclidean geometry, even in the absence of training in mathematics."
This stress on "spontaneous" discounts situated learning the tribe provides for its members. Even the BETTER performance of Mundurucu people on some geometric tasks (geometry of the sphere) did not convince the researchers the tribe's learning methods may actually work well; instead, they concluded that Westerners mess up their kids' innate intuitions. The youngest Western child they studied was five, I think - by this time, a lot of learning already takes place - and yet, again, what these younger kids knew was considered intuitive, compared to schooled US people.
Early exposure to math in the US not extensive compared to, say, exposure to language, but there is a lot going on in our culture geometrically, even if it's situated. In both cultures, success did not change much with age. But why does it mean that the geometry intuitions are innate, rather than developed within the culture before the age of five? After all, a five-year-old is typically fluent in her native language, but we don't conclude it's intuitive or innate on the basis of that evidence. I think the data, instead, confirms geometric intuitions don't change much with formal schooling. This reminded me of the paper, "School: Not where Americans learn their science" http://www.scribd.com/doc/44790217/Falk-and-Dierking-School-is-Not-Where-Americans-Learn-Science
I really liked the methodology of Socratic dialogues, where questions to Mundurucu were presented in terms of their surroundings, e.g. lines connecting villages or the geometry of a casaba rather than "sphere" (the word they don't have). I think the data researchers got was extremely valuable, and a lot of interesting things can be done with it going forward.
The site of the PI, Pierre Pica, is quite worth exploring: http://www.pierrepica.com/
What do you think?